1. Field of the Invention
The present invention relates to a variable capacity single headed piston-swash plate type refrigerant compressor mainly used for an air-conditioner for a car. More particularly, it relates to a variable capacity single headed piston-swash plate type compressor provided with a motion converting mechanism for converting a rotation of the swash plate into a reciprocation of the single headed pistons and effectively preventing a local abrasion of the reciprocating pistons and/or cylinder bores of the compressor to thereby obtain a reliable and long-life compression operation of the variable capacity compressor.
2. Description of the Related Art
A typical conventional variable capacity single headed piston-swash plate type compressor is disclosed in Japanese Unexamined ( Kokai ) Patent publication No. 60-175783 published on Sep. 9, 1985, by the Japanese Patent Office, whose corresponding U.S. Pat. No. 4,664,604.
FIG. 8 illustrates a compressor corresponding to the compressor of this publication. The compressor of FIG. 8 has a cylinder block 82 encased in a cylindrical shell 80, and provided with a plurality of cylinder bores 81. The cylindrical shell 80 defines a closed crank chamber 83 therein located axially in front of an inner end of the cylinder block 82. The crank chamber 83 is closed by a front housing 84 holding a radial bearing to support an outer portion Of a drive shaft 89. Rear ends of the cylinder block 82 and the cylindrical shell 80 are commonly closed by a rear housing 86 via a valve plate 85. The rear housing 86 is provided with an annularly extended suction chamber 87, and a cylindrical discharge chamber 88 communicated with the plurality of cylinder bores 81 of the cylinder block 82. The cylinder block 82 is centrally formed with a shaft bore in which a radial bearing is seated to rotatably support an inner end of the shaft 89. The drive shaft 89 has a central portion thereof on which a rotary support 90 is mounted to be rotated with the shaft 89 about the axis of the drive shaft 89 within the crank chamber 83. The rotary support 90 is connected with a swash plate 93 via a hinge mechanism 91, which includes an elongated aperture 91a formed in the rotary support 90, and a hinge pin 93b fixed to a swing plate 93a to be engaged in the elongated aperture 91a; The swing plate 93a is projected from a front face 93d of the swash plate 93, a rear face 93c of which faces an inner end of the cylinder block 82. As shown in FIG. 9, the swash plate 93 is slidably mounted on a spherical sleeve element 92 axially slidably mounted on the drive shaft 89. Namely, the swash plate 93 can be rotated together with the drive shaft 89 and slide on the spherical sleeve element 92 to change an angle of inclination with respect to a plate vertical to the drive shaft 89. The swash plate 93 is engaged with each of pistons 94 slidably fitted in the cylinder bores 81, via a pair of shoes 95 having a half-sphere shape. Each of the pair of shoes 95 has a flat face 95a engaged with the front or rear face 93d or 93c of the swash plate 93 and a spherical portion 95b slidably engaged with a spherical recess 94a formed in a frontmost portion of the piston, as shown in FIG. 9.
The cylinder block 82 is provided with a passageway 96 for providing a fluid communication between the crank chamber 83 and the suction chamber 87, and the passageway 96 can be closed and opened by a control valve 97.
When the drive shaft 89 is rotated by a drive force such as a force given by a car engine, the swash plate 93 is rotated together, and the pistons 94 are driven to perform a reciprocating movement in the cylinder bores 81. Namely, the rotation of the swash plate 93 is converted to a reciprocatory sliding movement of the piston 94 in the cylinder bore 81 by the pair of shoes 95 performing a complicated movement between the swash plate 93 and the piston 94. Namely, during the rotation of the swash plate 93, each shoe 95 slides, at the flat face 95a thereof, on the front or rear face 93d or 93c of the swash plate 93 along an ellipsoidal locus, and turns, at the spherical portion 95b thereof, in the spherical recess 94a of the piston 94 about the center of the spherical recess 94a of the piston 94. The sliding movement of the shoe 95 taking the ellipsoidal locus includes a first circumferential sliding movement relative to a plane lying in the front or rear face 93d or 93c of the swash plate 93, indicated by an arrow "A" in FIG. 9, and a second radial sliding movement relative to the same plate, indicated by an arrow "C" in FIG. 9. The rotating movement of the shoe 95 in the spherical recess 94a of the piston 94 is indicated by an arrow "B". The combination of the sliding and rotating movements of the shoe 95 contributes to the conversion of the rotation of the swash plate 93 into the reciprocation of each piston 94, and thus the reciprocation of the respective pistons 94 compresses a refrigerant gas pumped from the suction chamber 87 into the cylinder bores 81, and delivers the compressed refrigerant gas from the cylinder bores 81 toward the discharge chamber 88, from which the compressed refrigerant gas is further discharged toward an air-conditioning or refrigerating circuit.
The entire amount of the refrigerant gas discharged from the compressor, i.e., the whole compression capacity of the compressor, is controlled by adjusting a pressure level in the crank chamber 83 due to controlling operation of a capacity control valve 97.
When the capacity control valve 97 is moved to a position establishing a fluid communication between the crank chamber 83 and the suction chamber 87 via the passageway 96, the pressure level in the crank chamber 83 acting as a back pressure against the pistons 94 is lowered, and thus the angle of inclination of the swash plate 93 is made larger. Consequently, the hinge pin 93b of the hinge mechanism 91 is moved in the elongated aperture 91a to a position radially farthest from the drive shaft 89, and the sleeve element 92 is axially slid on the drive shaft 89 toward the front side of the compressor to thereby turn the swash plate 93 to a position having a larger angle of inclination. Accordingly, the ellipsoidal locus of the sliding movement performed by the respective shoes 95 is made to lengthen the long diameter thereof, and the stroke of the respective pistons 94 is extended. Accordingly, the compression capacity of the compressor becomes large.
When the capacity control valve 97 is moved to a position preventing the fluid communication between the crank chamber 83 and the suction chamber 87 via the passageway 96, the pressure level in the crank chamber 83 is raised by a blow-by gas leaking from the cylinder bores 81 into the chamber 83, and thus the pressure acting as a back pressure against the pistons 94 is made high to reduce the angle of inclination of the swash plate 93 with respect to a plane perpendicular to the axis of the drive shaft 89. Accordingly, the hinge pin 93b of the hinge mechanism 91 is moved in the elongated aperture 91a to a position radially approaching the drive shaft 89, and the sleeve element 92 is slid on the drive shaft 89 toward the rear side of the compressor. Therefore, the swash plate 93 is turned toward an erect position thereof, and thus the ellipsoidal locus of the sliding movement performed by the respective shoes 95 is made to shorten the long diameter thereof, and the stroke of the respective pistons 94 is shortened. As a result, the compression capacity of the compressor becomes small.
With the above-mentioned reciprocation-drive mechanism of the pistons 94 of the variable capacity single-headed swash plate type compressor, since each of the shoes 95 is held in the spherical recess 94a of the piston 94, it is prevented from performing a random displacement. Nevertheless, as previously stated, the shoe 95 is permitted to slide on the front or rear face 93d or 93c of the swash plate 93 at the flat face 95a thereof along the ellipsoidal locus, and this ellipsoidal sliding movement of the shoe 95 results in a radial displacement thereof relative to the axis of the drive shaft 89 of the compressor. Therefore, when the compression of the refrigerant gas is performed by the piston 94 in the cylinder bore 81, and when the piston 94 receives a pressure of the compressed gas, the piston 94 transmits a corresponding force to the swash plate 93 via each shoe 95, which always includes an axial force component, and a radial force component transmitted in the radial direction with respect to the axis of the drive shaft 89 from the piston 94 to the swash plate 93 via the shoe 95. The extent of the latter radial force component changes depending on the angle of inclination of the swash plate 93, and due to the radial force from the piston 94 acting on the swash plate 93 via each shoe 95, the single headed piston 94 supported by the wall of the cylinder bore 81 at the cylindrical body portion thereof, but not supported at the frontmost portion thereof, comes into a tight contact with the wall of the cylinder bore 81 at a given portion thereof, and thus a local abrasion of the piston 94 and/or the wall of the cylinder bore 81 of the cylinder block 82 necessarily occurs, whereby a reliable long operation life of the compressor is prevented.